As for a wheel nut wrench, there are various types of wheel nut wrenches such as an open-ended type, a single-ended T shape, and a single-ended L shape. Among them, the single-ended L-shaped wheel nut wrench is constituted in a manner that a round bar (an inner filling body) made of carbon steel is used in general, a nut socket portion is formed at a tip thereof by hot forging, and then a side where this nut socket portion is provided is bent to an L shape. Among various types of wrenches such as this single-ended L-shaped wheel nut wrench, there is one sold as a single component, but most of them are each mounted in a vehicle as an accessory attached to the vehicle. Thus, the number of wrenches is enormous, and a significant cost reduction is required.
Thus, as for the single-ended L-shaped wheel nut wrench in particular, in contrast with a conventional wheel nut wrench made after a round bar is processed, a wheel nut wrench constituted in a manner that a nut socket portion is formed by cold forging with a tube made of carbon steel as a material, and a side where this nut socket portion is provided is bent to an L shape is well known in Japanese Patent Publication No. Hei 3-27297, Patent Document 1.
As for the conventionally well-known wheel nut wrench disclosed in above-described Patent Document 1, the material is a tube made of carbon steel of S45C, and furthermore the nut socket portion can be formed by cold forging, and therefore it makes it possible to reduce a manufacturing cost compared to the conventional wheel nut wrench with the round bar. However, in order to prevent that a thickness of the nut socket portion thins to thereby reduce strength, a process to make the nut socket portion thick is required, and it takes time for this process to be performed, so that a problem that a sufficient cost reduction cannot be achieved is caused.
The wheel nut wrench, in actual use, is used in such a way that a handle portion is hit with a hammer, a supporting tube is inserted into a handle portion, a foot or feet is/are put on a handle portion to apply a total body weight thereon, or the like, and thus, there is often a case that significant torsional pressure is applied on the nut socket portion.
Therefore, in the case when the single-ended L-shaped wheel nut wrench is manufactured with a tube, how deformation-resistant strength against torsional pressure on the nut socket portion is increased under a situation where processes are made as easy as possible is a next issue.